It is generally accepted that moderate exposure to sunlight often has beneficial effects upon the human body. Apart from stimulating the circulation of blood and enhancing the formation of hemoglobin, exposure to sunlight is advocated in the treatment of tuberculosis of glands and bones and in the treatment of certain skin diseases, such as acne and psoriasis and is necessary for the in vivo formation of Vitamin D.
Overexposure to sunlight, however, may produce adverse effects, the best known of which is sunburn, with symptoms ranging from a reddening of the skin (erythema) to painful burns and blistering. More serious are effects produced in certain individuals, such as sailors and farmers, who are frequently exposed to intense sunlight. These effects include premature aging of the skin, certain types of dermatitis, and even skin cancer.
Protection of human skin against the harmful effects of sunlight can be accomplished by applying a sunscreening preparation to the skin. Many such preparations are known. In general, they contain various natural and/or synthetic compounds or materials which act as sunscreening agents by absorbing harmful erythema-producing radiation. Sunscreening agents should prevent the penetration of radiation of wavelengths between 290 mm and 315 mm, but should transmit radiation within the 315-400 mm range, which promotes tanning. Increased protection can be achieved by using compounds with a wider absorption capacity, and also by adjusting the percentage of the UV absorber used. It is also important that the sunscreening preparation be non-toxic and mild to the skin.
Substances which have been used as sunscreening agents include p-aminobenzoic acid and its derivatives, salicylates, cinnamic acid derivatives, coumarin derivatives, quinone salts, quinoline derivatives, tannic acid and its derivatives, hydroquinone and benzophenone derivatives. Still others are disclosed in Karg, U.S. Pat. Nos. 3,895,104, Strobel, 3,875,198, 3,878,229 and 3,879,443, Gerecht, 3,864,474, Norman, 3,574,825, Della Lane et al, 3,532,788, Fitzi et al, 3,624,075, Doner, 3,670,074, Welters et al, 3,781,417, Inazuka et al, 3,929,819, Richardson, 3,751,563, Catino, 3,705,234, Madigan, 3,697,642, Klaui et al, 3,920,834, the article "Sunscreens Safe and Effective Cosmetic-Drugs", by William R. Markland, COSMETICS AND TOILETRIES, March 1976, pages 79-81, and "Cosmetics" by Sagarin, Interscience Publishers, 1959, Chapter 8, pages 189-212.
Naturally occurring materials which are effective sunscreening agents include extracts of hyperium flowers, chamomile flowers, aloe leaves, helichrysum flowers, frangula bark and nut extracts, e.g., walnut husk and leaves. For more detailed information, see the article entitled "Natural Sunscreens: Vegetable Derivatives as Sunscreens and Tanning Agents", in COSMETICS AND TOILETRIES, March, 1976, pages 34-36.
It has now been surprisingly discovered that hops contain certain selective UV absorbents which act as effective sunscreening agents in the prevention of sunburn. Hops are the flower of the perennial vine, humulus lupulus. Many compounds have been identified in hops, of which the class known as the humulones are known to be most important for beer flavor. During the processing of barley malt to make beer, these humulones are isomerized to the more soluble isohumulones, which are the actual flavoring components present in all beers.
It has now been found that an extract of hops, when dissolved or dispersed in an aqueous, alcoholic or oily medium, or in a froth, and applied to the skin before exposure to the sun, effectively delays or prevents the painful effects known as erythema, or sunburn, while permitting the penetration of ultraviolet radiation which permits the formation of a sun tan. By way of illustration, the hop extract can be obtained by extracting hops with an organic solvent, such as methylene chloride or hexane, for example, recovering the hop extract from the solvent and incorporating the extract into a sunscreening composition, or the hop extract can be extracted with an alcohol or oil useful as an ingredient in sunscreening compositions and incorporated directly into the composition.
The ultraviolet absorption spectrum of many hop compounds are known and are even used in the evaluation and analysis of hops. But hop compounds have not been previously known to act as sunscreens. The effectiveness of a sunburn preventive requires not only certain ultraviolet absorbing properties, but also stability on the skin and in the presence of sunlight and perspiration, non-toxicity to animal life and the non-irritation of human skin. These additional properties have now been found to be present in hop extracts.